Renal effects of bumetanide.

Effects of bumetanide (2.5, 25 and 250 microgram/kg i.v.) on renal hemodynamics and function were investigated in anesthetized dogs using clearance methods, stop-flow analysis and radioactive microsphere. Under conditions of mild isotonic saline loading, significant diuresis was observed within 5 min after the injection of 25 and 250 microgram/kg of the drug, and with the higher dose, a maximal fractional sodium excretion of 34% was observed. The dose of 250 microgram/kg of bumetanide caused a significant 44% increase in blood flow 5 min after the injection. In a hydropenic condition, the reabsorption of free water was significantly reduced, thus suggesting an inhibitory effect on the ascending limb of Henle's loop. In stop-flow experiments, inhibition of sodium reabsorption at the distal tubule was evident. Bumetanide increased blood flow in the juxtamedullary more so than in the superficial area. The increased blood flow in the juxtamedullary area also may contribute to the diuretic action of bumetanide through enhancement of the countercurrent exchange system in the renal medulla.